1. Field of the Invention
The present invention relates to a pulley structure of a belt type electric power steering (EPS) gear, and more particularly, to a pulley structure of a belt type EPS gear capable of providing good assemblability using an engineering plastic and a specific structure.
2. Discussion of Related Art
A power steering apparatus for a vehicle functions to assist with a steering force such that a driver can steer a handle with a small force when steering the vehicle. In power steering apparatuses, an apparatus using a method utilizing a rotating force of a motor having a function of assisting with the steering force is referred to as an electric power steering (EPS) apparatus.
The EPS apparatus detects the steering force of the driver and rotates the motor to assist with the steering force in a direction in which the driver wants to steer. In the EPS apparatus, a belt type EPS apparatus for transmitting a rotating force of a motor shaft through a timing belt uses the timing belt as a unit that connects the motor shaft to a rack bar driving apparatus to reduce a rotating speed of the motor shaft and transmit the rotating force.
A pulley is used to transmit the driving force of the belt to a ball nut, and a conventional pulley structure has a structure to be described below.
FIGS. 1 and 2 show a nut pulley structure of a conventional belt type power steering gear, illustrating a nut pulley 1 including a flange 3 configured to prevent separation of a driving section 2 of a belt from the belt. The nut pulley 1 is connected to a ball nut 5, and one side surface of the nut pulley 1 comes in contact with a fixing section 4 to be fixed thereto.
FIG. 1 shows a state in which the nut pulley of the conventional belt type power steering gear is coupled to the ball nut 5, and FIG. 2 is a view for describing a coupling method of the nut pulley 1 and the ball nut 5.
A tolerance ring 6 is disposed at one side surface of the ball nut to cross the ball nut, and coupled in a manner in which the nut pulley 1 is press-fitted to be fixed by a 3-dimensional structure of the tolerance ring 6. The tolerance ring 6 having a protrusion shape is disposed in a direction opposite to a circumferential direction of the ball nut 5, and the tolerance ring 6 is coupled to an inner surface of the nut pulley 1 to be fixed by the fixing section 4.
Since the conventional gear pulley structure cannot be easily manufactured with a flange integrated with the nut pulley using a sintered material, a press-fitting process of the flange should be separately performed.
In addition, a metallic material is used to excessively increase the weight, and weight reduction of the belt type power steering is severely limited.